Complex interconnected electronic systems are increasingly present in our daily lives, and their failure can have serious consequences in human, economic, and social terms, especially for critical applications requiring reliable operation.
It is for this reason that wire networks are now regarded as critical systems and their diagnosis is beginning to be a consideration in industry.
With the rise in total cable length (about 4 km in modern cars and up to 400 km in passenger aircraft) and the increasing sensitivity to network faults because of design complexities, various problems due to electrical cables may arise at the system level.
Network diagnosis is therefore essential for detecting and locating these faults.
Today, for example, a mechanic may take up to two days to find and repair a wiring fault, sometimes after changing healthy and costly components (ECU, connector, etc.). For example, 70% of the ECUs returned to the manufacturer are free of faults.
In the field of aeronautics, the operating loss from an AOG (Aircraft On Ground) grounded for repair is close to €1 to 2 million per day.
At present, the most promising and most widely used technique for diagnosing wiring harnesses or bundles is reflectometry.
Reflectometry is based on a technique similar to that of a radar system.
In particular, a wide spectral band signal is injected into the bundle and a portion of the signal is reflected back to the point of injection by each area having a variation in the characteristic impedance of the line (discontinuity, for example) that is encountered by the signal. Of course, in the following, the term “reflected” is understood to mean one or more electrical signals returned by the transmission medium used to transmit the wide spectral band signal.
This produces a series of echoes whose amplitudes depend on the topology of the bundle and on the faults that may be present therein. Analysis of these amplitudes allows identifying the nature of the faults: whether they are hard faults, such as open circuits or short circuits, or soft faults (localized but regular variations from the characteristic impedance).
Analysis of the return time of echoes at the injection site provides information about the position of faults in the bundle.
Document US 2011/0153235 provides a method for detecting faults in wiring by graphically modeling the expected responses and performing a comparison to actual responses. In FIGS. 8 and 9 of that document, reference 902 indicates the detection of a difference exceeding a threshold, representative of a fault. In practice, however, when the bundle has multiple divisions, it may not be easy to pinpoint the fault location.
In any event, ambiguity remains concerning the position of the fault in many cases. For example, if a fault occurs beyond a splice, in other words beyond a division of the bundle into multiple branches, it is impossible to find the right branch quickly and simply when using measurements at a single point. This ambiguity is a problem during maintenance and repair, with an economic impact that can be significant for some areas of application.
Document WO 2010/043602 A1 discloses a method of distributed reflectometry that eliminates ambiguity when locating a fault in a complex bundle, by multiplying the measurement points in the network. More particularly, the complete reflectometry system (signal generation, acquisition, processing) is duplicated in order to inject a signal at the ends of the cable bundle. A diagnosis is therefore made from each end.
In the embedded case, the system is duplicated at each end. In the case of manual intervention, the ambiguity is only eliminated after multiple operations, such as the additional removal of vehicle trim elements by the technician. This method also requires communication in order to synchronize measurements between the various units.
All of this means a considerable loss of time and money.